The covalent functionalization of metallic single-walled carbon nanotubes (CNTs) with transition metal phthalocyanines (MPc, with M = Mn, Fe and Co) are addressed by density functional calculations. The CNT-MPc catalytic activity toward the oxygen reduction reaction (ORR) is investigated through the O-2 stretching frequency adsorbed on the phthalocyanine metal center. We find better reduction abilities when the CNT functionalization occurs through sp(2)-like bonds. Multiple stable-spin states for the M-O-2 adduct are also found for M = Mn and Fe, suggesting higher ORR rates. The CNT-MPc complexes show metallic characteristics, suggesting favorable conditions to work as ORR cathode catalysts in fuel cells. (C) 2012 Elsevier B. V. All rights reserved.